The present invention relates to a method for efficiently utilizing a geographical identifier in a network for activating a plurality of movable hosts and a network that corresponds to the plurality of movablehosts As a network for supporting a plurality of movable hosts, there has been known a network configured for defining the following two identifiers and managing the correspondence for each identifier for supporting the movable host. Two identifiers are a logical identifier and a geographical identifier. The logical identifier that identifies a mobile host itself, being independent of a point of the mobile host connecting with a subnetwork. The geographical identifier that indicates a location of a mobile host, being dependent of a point of the mobile host connecting with a subnetwork. (See Okanoue, Osawa, Gotoh, and Komatsu, "IP Mobility with Double IP Header", Proceedings of Institute of Electronics Information and Communication Engineers, IN95-64, Vol.95, No.269, September 1995) (referred to as a writing 1). This network is configured to separate a network layer into sublayers based on a logical identifier and a geographical identifier and encapsulate a packet with a logical identifier based header added thereto by using a geographical identifier based header for realizing communications with a movable host.
This network includes one or more nodes for supporting the movable host provided with the logical identifier and the geographical identifier. The node is called agent. The agent is categorized into two, an home agent (referred to as HA, hereinafter) and a foreign agent (referred to as FA, hereinafter). The sub network configured on the logical identifier of each movable host is defined as a home network (referred to as HN, hereinafter).
The HA is located on the HN of each movable host. Each time the movable host is moved to another sub network, the logical identifier and the geographical identifier are registered in the HA. Hence, the HA provides a capability of managing the location information of the movable host whose agent is constantly the HA.
On the other hand, the FA is located at each sub network for supporting the movable host and provides a capability of supporting communications with all movable hosts located in the sub network. When the movable host is moved to another sub network, the movable host serves to set the agent of the sub network to the FA and register the logical identifier and the geographical identifier to the FA. A host that is communicating with the movable host is capable of managing a pair of a logical identifier and a geographical identifier of the subject movable host.
FIG. 8 illustrates how the movable host manages the logical identifier and the geographical identifier. In FIG. 8, numerals 1000 to 1002 denote sub networks. Numerals 1003 to 1005 denote agents. A numeral 1006 denotes a movable host. A numeral 1009 denotes an opposite host with which the movable host 1006 is communicating. The sub network 1000 is the HN of the movable host 1006. The agent 1003 is the HA of the movable host 1006. The movable host 1006 uses home-1 that depends on the HN of the sub network 1000 as the logical identifier. In this configuration, the description will be oriented to the movement of the movable host 1006 from the sub networks 1001 to 1002 as keeping communication with the opposite host.
When the movable host 1006 moves to the sub network 1002, the identifier, location-1, depending on the sub network 1002 is used as the geographical identifier of the movable host 1006. At this time, the agent 1005 located in the new sub network 1002 is set to the FA of the movable host 1006. The pair of the logical identifier and the geographical identifier (home-1 and location-1) of the movable host 1006 is notified to the agent 1003 that is the HA of the movable host 1006 and the agent 1005 that is the FA of the movable host 1006. The pair of the logical identifier and the geographical identifier (home-1 and location-1) of the movable host 1006 is notified to the opposite host 1006 with which the movable host is communicating through the communication executed between both of the hosts.
In the conventional system, a plurality of movable hosts located in one sub network utilize their own geographical identifiers that are different from each other. This environment is shown in FIG. 9. In FIG. 9, numerals 1100, 1110, and 1120 denote sub networks. Numerals 1130 and 1140 denote movable hosts. The movable host 1130 is located in the sub network 1110. The movable host 1140 is located in the sub network 1120. The movable host 1130 uses (H1, B2) as the pair of a logical identifier and a geographical identifier. The movable host 1140 uses (H2, C3) as the pair of a logical identifier and a geographical identifier. When the movable hosts 1130 and 1140 move to the sub network 1100, the movable host 1130 uses (H1, A1) as the pair of a logical identifier and a geographical identifier. The movable host 1140 uses (H2, A2) as the pair of a logical identifier and a geographical identifier.
Where a plurality of movable hosts are concurrently located in one sub network, it is necessary to provide the same number of geographical identifiers as the number of movable hosts concurrently existing in the sub network. Therefore, the conventional system has a drawback of bringing about a shortage of geographical identifiers and thereby disabling to support one or more movable hosts newly relocated from another sub network.